The present invention relates to method for producing an iron golf club head, and more particularly relates to an improvement in the production of an iron golf club head with FRP backing.
Various types of iron golf club heads are available in the marketplace. In one example, an iron golf club head has a main body fully made of a metallic material such as stainless, cast iron and brass. In another example, an iron golf club head has a composite main body in which the sole and core made of metal is fully covered with FRP (fiber reinforced plastic), in particular with CFRP (carbon fiber reinforced plastic). In the case of this composite type, the face side covered with a FRP shell imposes high repellent to balls, thereby causing long distance shots. Further, the weight of the iron golf club head is greatly reduced and shooting direction of balls is significantly stabilized.
In the case of the fully metallic iron golf club head, limited properties of the metallic material cannot assure variety in feeling at shots. In addition, uniform specific gravity of the metallic material does not allow local weight adjustment and, as a consequence, adjustment of inertia moment.
In the case of the composite iron golf club head, the FRP shell on the face side is quite vulnerable to striking shock at shooting balls. Biased weight on the side of the sole causes unbalanced weight distribution with less contribution to adjustment of inertia moment.
In order to resolve the above problems, other inventions added a highly elastic backing containing reinforcing fibers to the face side of an iron golf club head. Such a metal-FRP composite structure well shields the FRP component against external attack and improves feeling at shots. The shift of weight saved by addition of the backing can be alloted to sections of the main body other than the face side, thereby enabling adjustment of inertia moment without any increase in weight.
In production of such a composite iron club head, a rear recess is formed in the surface of the main body opposite to the face side, a FRP plate is placed in and bonded to the rear recess. The FRP plate is locked into place by a presser ring in order to prevent fall of the FRP plate at shooting balls. Since presence of the recess causes reduction in weight of the main body, the thickness of the main body in the shooting direction can be increased without causing any substantial increase in weight. Thus, the weight of the main body may be dispersed off its center of gravity for easy adjustment of inertia moment.
Despite these merits, however, use of the solid FRP plate as a backing is inevitably accompanied with poor bonding between the two solid component, i.e. the iron main body and the FRP plate. This poor bonding seriously mars function of the FRP component in the composite structure. When the presser ring provides insufficient locking, the FRP plate in the rear recess tends to fall due to shock at shooting balls.